The present invention relates to image bearing templates for masking or otherwise modifying the light image to which photographic film is exposed in a camera, and more particularly, it concerns such templates adapted to be used with instant film packs.
The current state-of-the-art relative to information or image bearing templates of the general class which includes the present invention are exemplified by the disclosures of U.S. Pat. Nos. 3,916,423--Ueda et al and 4,268,144--Wheeler. In both of these patents, a substantially transparent template or mask having light blocking information or images thereon are adapted to be inserted in the exposure window of commercially available instant film packs in which each of a succession of individual film units supplied in the pack are advanced to the camera focal plane as established by the top wall of the pack housing in which the exposure window is formed.
In the Ueda et al patent, the template or mask is formed by a relatively thick and rigid plate of glass or similar material. In one form, the rigid template of Ueda et al is a rectangular body dimensioned the same as the exposure window with four outwardly directed projections on the side edges intended to stress the material of the film pack housing forming the exposure window to hold the template in place. In another form of the rigid template of Ueda et al, insertability of the rigid plate into the film pack window is enabled by forming the major body of the plate with peripheral dimensions somewhat smaller than the film pack window so that tabs projecting from opposite sides of the plate can be inserted through the window and will underlie the wall of the pack housing in which the window is formed. The thickness of the plate causes diffraction of the subject image and results in displacement of the objective focal plane from the surface of the uppermost film unit in the pack. Sharpness of the subject image can be accommodated by a combination of restricting the thickness of the tabs holding the plate in the window and selecting the index of refraction of the material from which the plate is formed to correct for displacement of the objective focal plane from the surface of the uppermost film unit.
The Wheeler patent employs a relatively thin and pliant template having projecting tabs extending from three sides and adapted to underlie the pack wall in which the exposure window is formed. To retain the template against movement in one direction with an underlying film unit as the latter is ejected from the pack housing for processing after exposure, the leading edge of the template is formed with a central, generally up-struck limit tab. To otherwise orient the template in relation to the exposure window Wheeler relies on edge portions of the thin sheet which, of necessity, fit within the pack with clearance space between the template edges and the side walls of the film pack. Also, insertion and removal of the Wheeler template requires manipulation at the image surface of the template.
In light of the prior art, there exists a need for a thin image bearing template which does not distort or rely upon the resiliency of the exposure window frame in a film pack for retention or insertion of the template, which insures both longitudinal and lateral positioning support of the template in the exposure window and which facilitates insertion and removal of the template without excessive manual contact with the image surface of the template.